De-inking of waste paper

ABSTRACT

In the production of pulp and paper from starch-containing paper, the deinking effect can be improved by including treatment with both a starch-degrading enzyme and a pectate lyase. The process comprises enzyme treatment during or after disintegration of the paper to produce pulp, followed by separation of ink particles.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. application Ser. No.09/826,691, filed on Apr. 5, 2001, the contents of which are fullyincorporated herein by reference.

TECHNICAL FIELD

[0002] This invention relates to processes for removing inks, coatingsand toners during the recycling of starch-containing waste papers usingboth a starch-degrading enzyme and a pectate lyase. More particularly,it relates to such processes leading to improved brightness andcleanliness of the pulp or paper.

BACKGROUND ART

[0003] In the recycling of waste paper it is usually desirable to removethe printing ink in order to produce new paper of high brightness andimproved cleanliness. The term “cleanliness” relates to a lack of or areduced amount of residual ink particles in the pulp and/or paperproduced from these pulps. Some of the higher quality grades of paperincluding mixed office waste have seen a lower rate of reuse compare toother grades, such as old corrugated cardboard. This is due to thedifficulty of removing polymeric inks, coatings and toners such asnon-contact, fused laser-prints, xerographic toners, UV/EB cured inks,varnish overlays and coated paper. It is conventional to repulp (ordisintegrate) the old paper together with deinking chemicals, such asdeinking surfactant, NaOH and sodium silicate, combined withbleaching/brightening with hydrogen peroxide and deinking chemicals andby separation of ink particles from the pulp. However, standard chemicaldeinking agents may not work well for laser ink and xerographic tonerremoval.

[0004] Enzymatic methods have been described in the prior art to improveremoval of ink and thereby increase the brightness and the cleanlinessof the pulp produced from this process.

[0005] An amylase, i.e. a starch-degrading enzyme has been described inU.S. Pat. No. 5,879,509 (Novo Nordisk) to improve the deinking effect.Pectinases are disclosed in U.S. Pat. No. 5,785,809 (KRICT) to dislodgeink particles from waste paper. Furthermore, the use of endo-pectatelyase in the pulping of kozo (Japanese paper mulberry, Broussonetiakazinoki Sieb) has been described by Kobayashi Y et al.(1984), MokuzaiGakkaishi, 30, 848-56.

[0006] It is the object of this invention to provide an improved processfor removal of printing ink and increasing brightness and cleanliness ofthe pulp and paper for use in the recycling of starch-containing wastepaper.

STATEMENT OF THE INVENTION

[0007] We have found that in the production of pulp and paper fromstarch-containing printed paper, the deinking effect can be improved byincluding treatment with both a starch-degrading enzyme and a pectatelyase.

[0008] Accordingly, the invention provides a process for producing apapermaking pulp from starch-containing printed paper, comprising thefollowing steps:

[0009] a) disintegrating the paper to produce a pulp,

[0010] b) treating with a starch-degrading enzyme and an pectate lyaseduring or after step a), and

[0011] c) separating ink particles from the pulp after steps a) and b).

[0012] The invention also provides a process for recycling oldstarch-containing printed paper into new paper or tissue, comprisingproducing a pulp by the above process, followed by paper- ortissue-making.

DETAILED DESCRIPTION OF THE INVENTION

[0013] In the context of the present invention the term “improveddeinking effect” and “improved process,” indicates that the brightnessand cleanliness of any paper produced from the deinked pulp isincreased/enhanced in comparison to paper produced from pulps which havenot been treated according to the present invention.

[0014] Starch-Containing Printed Paper

[0015] The process of the invention is applicable to the recycling ofany kind of printed, starch-containing paper. Examples include oldnewspaper, magazines, mixed and sorted office waste and papers printedusing laser or Xerographic methods. The paper may contain mineralfillers such as calcium carbonate and clay.

[0016] The starch used in the manufacture of these papers may consist ofstarch from any source and generally contains 20-30% of amylose and thebalance amylopectin. Examples include corn starch, wheat starch, potatostarch, rice starch and tapioca starch. When used as a coating or sizingmaterial, the starch to be used will generally be pretreated to achievea limited hydrolysis by cooking with amylase or acid.

[0017] The starches used in the paper manufacturing process may alsoconsist of modified starch. Modified starches useful for paper coatinginclude dextrin (e.g. white dextrin, canary dextrin or British gum),acid-modified starch, oxidized starch (chlorinated starch),hydroxyethylated starch and cationic starch

[0018] The inks to be removed by the process of this invention includebut are not limited to non-contact laser inks, xerographic toners,letterpress ink generally used in printing newsprint, magazine print,offset printing ink, ultraviolet or electron beam cured ink.

[0019] Disintegration

[0020] The disintegration step may be performed in a conventionalpulper, typically for 5-30 minutes at 3-30% pulp consistency.

[0021] Conventional deinking chemicals typically comprise an alkalinereagent and a surfactant. The surfactant can, e.g., be used at a dosageof 0.025-0.6%, preferably 0.030-0.15%. The surfactant is preferablynonionic in nature, e.g. ethoxylated octyl or nonyl phenol or any of thenonionic surfactants disclosed in Park et al., 1992, Biotechnology andBioengineering 39:117-120. The alkaline reagent may be NaOH (e.g.0.2-5%, preferably 0.5-1%) and/or sodium silicate (e.g. 0.4-5%,preferably 0.5-2%). The alkaline reagents are usually added to a pH of8-12, preferably 10-11.5. The deinking chemicals may further comprisemagnesium sulfate, and hydrogen peroxide.

[0022] If the enzyme treatment is performed during or after thedisintegration, it may be preferable to modify the addition of deinkingchemicals (as described further below) in order to provide suitableconditions for the action of the enzyme, and particularly to reduce oravoid the addition of alkaline reagent to achieve a pH, which issuitable for the enzyme action.

[0023] Starch-Degrading Enzyme

[0024] The starch-degrading or amylolytic enzyme is preferably anamylase, e.g. an A-amylase, a glucoamylase or a debranching enzyme. Asingle enzyme or a combination may be used, e.g. Δ-amylase together withglucoamylase and/or a debranching enzyme. It is preferred to perform theenzyme treatment at an alkaline pH in the range 6-10, preferably 8-10and to use an enzyme, which is alkaline stable and active in this rangeand preferably has optimum activity in this range.

[0025] Examples of preferred Δ-amylases are those derived from strainsof Bacillus, e.g. B. amyloliquefaciens (B. subtilis), B. licheniformisor B. stearothermophilus and from strains of Aspergillus, e.g. A.oryzae. Examples of commercial products are BAN™, Termamyl®, AquazymeUltra™ and Fungamyl™ (products of Novozymes A/S).

[0026] Glucoamylase derived from a strain of Aspergillus niger ispreferred, e.g. the commercial product AMG (product of Novozymes A/S).

[0027] The debranching enzyme is preferably a pullulanase, particularlyone derived from a strain of Bacillus acidopullulyticus, e.g. thecommercial product Promozyme® (product of Novozymes A/S).

[0028] Suitable conditions for Bacillus amylase may be pH 4-10,20θ-90θC, preferably pH 6-10, 40θ-70θC. Suitable conditions for A.oryzae amylase may be pH 3-8, 20θ-70θC, preferably pH 5-6.

[0029] Pectate Lyase

[0030] The Pectate lyase (EC 4.2.2.2) is an enzyme which catalyse therandom cleavage of α-1,4-glycosidic linkages in pectic acid (also calledpolygalacturonic acid) by transelimination. Pectate lyases also includepolygalacturonate lyases and poly(1,4-α-D-galacturonide) lyases. Asingle enzyme or a combination of pectate lyases may be used.

[0031] It is preferred to perform the enzyme treatment at a pH of 6-10,more preferably pH 8-10 and a temperature of 25-80θC, more preferably35-55θC. The use of precipitated calcium carbonate in some types ofpapers mentioned above assures an adequate calcium ion level for theaction of certain of the amylases also mentioned earlier.

[0032] Examples of preferred pectate lyases are those that have beencloned from different bacterial genera such as Erwinia, Pseudomonas,Klebsiella, Xanthomonas and Bacillus, especially Bacillus licheniformis(U.S. Pat. No. 6,124,127), as well as from Bacillus subtilis (Nasser etal. (1993) FEBS Letts. 335:319-326) and Bacillus sp. YA-14 (Kim et al.(1994) Biosci. Biotech. Biochem. 58:947-949). Purification of pectatelyases with maximum activity in the pH range of 8-10 produced byBacillus pumilus (Dave and Vaughn (1971) J. Bacteriol. 108:166-174), B.polymyxa (Nagel and Vaughn (1961) Arch. Biochem. Biophys. 93:344-352),B. stearothermophilus (Karbassi and Vaughn (1980) Can. J. Microbiol.26:377-384), Bacillus sp. (Hasegawa and Nagel (1966) J. Food Sci.31:838-845) and Bacillus sp. RK9 (Kelly and Fogarty (1978) Can. J.Microbiol. 24:1164-1172) have also been described. Any of the above, aswell as divalent cation-independent and/or thermostable pectate lyases,may be used in practicing the invention.

[0033] A preferred pectate lyase may be obtained from Bacilluslicheniformis as described in U.S. Pat. No. 6,124,127.

[0034] Other pectate lyases could be those that comprise the amino acidsequence of a pectate lyase disclosed in Heffron et al., (1995) Mol.Plant-Microbe Interact. 8: 331-334 and Henrissat et al., (1995) PlantPhysiol. 107: 963-976.

[0035] It will be understood that any polypeptide exhibiting pectatelyase activity may be used in practicing the invention. That is, pectatelyases derived from other organisms, or pectate lyases derived from theenzymes listed above in which one or more amino acids have been added,deleted, or substituted, including hybrid polypeptides, may be used, solong as the resulting polypeptides exhibit pectate lyase activity.Pectate lyases for use in the invention may be derived from their cellof origin or may be recombinantly produced, and may be purified orisolated. As used herein, “purified” or “isolated” pectate lyase ispectate lyase that has been treated to remove non-pectate lyase materialderived from the cell in which it was synthesized that could interferewith its enzymatic activity. Typically, the pectate lyase is separatedfrom the bacterial or fungal microorganism in which it is produced as anendogenous constituent or as a recombinant product. If the pectate lyaseis secreted into the culture medium, purification may compriseseparating the culture medium from the biomass by centrifugation,filtration, or precipitation, using conventional methods. Alternatively,the pectate lyase may be released from the host cell by cell disruptionand separation of the biomass. In some cases, further purification maybe achieved by conventional protein purification methods, includingwithout limitation ammonium sulfate precipitation; acid or chaotropeextraction; ion-exchange, molecular sieve, and hydrophobicchromatography, including FPLC and HPLC; preparative isoelectricfocusing; and preparative polyacrylamide gel electrophoresis.Alternatively, purification may be achieved using affinitychromatography, including immunoaffinity chromatography. For example,hybrid recombinant pectate lyases may be used having an additional aminoacid sequence that serves as an affinity “tag”, which facilitatespurification using an appropriate solid-phase matrix.

[0036] The pectate lyases used in the methods of the invention may bechemically modified to enhance one or more properties that render themeven more advantageous, such as, e.g., increasing solubility, decreasinglability or divalent ion dependence, etc. The modifications include,without limitation, phosphorylation, acetylation, sulfation, acylation,or other protein modifications known to those skilled in the art.

[0037] Enzyme Treatment

[0038] Normally, the enzyme treatment will consist of a simultaneouslytreatment with a starch-degrading enzyme and a pectate lyase during orafter disintegration, but it may consist of treatment with astarch-degrading enzyme first and a pectate lyase later during or afterdisintegration or vice versa.

[0039] In the following the term enzyme treatment refers to simultaneoustreatment with a starch-degrading enzyme and a pectate lyase, treatmentwith a starch-degrading enzyme first followed by treatment with apectate lyase later or vice versa.

[0040] The process conditions are selected so as to increase thebrightness and cleanliness of the pulp after the deinking and thebrightness and cleanliness of the paper produced from this pulp.Preferred process conditions are at pH 6-10, more preferably pH 8-10,most preferably pH 8-9 and a temperature at 25-80θC, more preferably35-55θC. A preferred reaction time may be found in the range 10 min-24hours, particularly 10 min-3 hours at an amylase dosage of 0.01-10 KNU/gdry matter (1 KNU=1000 NU, which is described below), preferably 0.02-3)KNU/g of dry matter and a pectate lyase dosage of 0.01-10 APSU/g of drymatter, preferably 0.05-5 APSU/g of dry matter.

[0041] Disintegration and Enzyme Treatment

[0042] Preferably, the enzyme treatment may be performed simultaneouslywith disintegration. In this case the enzyme treatment may optionally becontinued by holding the pulp after the disintegration.

[0043] The enzyme treatment is preferably performed in the presence of asurfactant, and in the case of an Δ-amylase from Bacillus and a pectatelyase from Bacillus it is preferred to add alkaline reagents (typicallyNaOH or sodium carbonate) to achieve a suitable pH, e.g. pH 6-10(preferably 8-10).

[0044] The disintegration and enzyme treatment will occur before the inkseparation, which can be followed by conventional bleaching withhydrogen peroxide and deinking chemicals. Preferably, separation of inkparticles is performed both before and after the bleaching.

[0045] The enzyme treatment may also be performed by addition of enzymeto the pulp after disintegration. In a preferred embodiment, this isperformed simultaneously with hydrogen peroxide bleaching, preferably inthe presence of a surfactant. In the case of simultaneous bleaching andtreatment with an Δ-amylase from Bacillus and a pectate lyase fromBacillus it is preferred to add 0.5-2% H₂O₂ and alkaline reagents(typically NaOH and sodium silicate, e.g. 1-5% sodium silicate and0.5-5% NaOH) so as to achieve pH 9-10. The combined bleaching and enzymetreatment is preferably performed at 30θ-60θC for 1-3 hours.

[0046] Separation of Ink Particles

[0047] After the disintegration and enzyme treatment, ink particles maybe separated from the pulp in a conventional manner, such as bymechanical deinking, flotation, chemi-mechanical deinking, agglomerationchemistry (see e.g. McBride, Pulp and Paper, April 1994, Miller FreemanPublishers, San Francisco, p. 44), washing, cycles of dilution andfiltration, treatment in hydrolcyclones, or by a suitable combination ofthese.

[0048] Papermaking

[0049] After deinking according to the invention, the deinked pulp isgenerally mixed with other pulp, e.g. kraft pulp and mechanical pulpetc., before papermaking. The final paper- or tissue-making step can beperformed in a conventional paper- or tissue-making machine

[0050] Materials and Methods

[0051] Enzyme Activity

[0052] KNU:

[0053] The enzymatic activity measure used herein KNU (KNU=1000 NU) isdefined as the amount of enzyme which, under standard conditions (i.e.at 37θC+/−0.05; 0.0003 M Ca²⁺; and pH 5.6) dextrinizes 5.26 g starch drysubstance Merck Amylum solubile.

[0054] The enzymatic activity may be determined using potato starch assubstrate. This method is based on the break-down of modified potatostarch by the enzyme, and the reaction is followed by mixing samples ofthe starch/enzyme solution with an iodine solution. Initially, ablackish-blue color is formed, but during the break-down of the starchthe blue color gets weaker and gradually turns into a reddish-brown,which is compared to a colored glass standard.

[0055] APSU:

[0056] The APSU unit assay is a viscosity measurement using substratepolygalacturonic acid with no added calcium. The substrate 5% w/vpolygalacturonate acid sodium salt (Sigma P-1879) is solubilised in 0.1M Glycin buffer pH 10. The 4 ml substrate is preincubated for 5 min at40θC. The enzyme is added (in a volume of 250 Π) and mixed for 10 s on amixer at maximum speed, it is then incubated for 20 min at 40θC. For astandard curve double determination of a dilution of enzymeconcentration in the range of 5 APSU/ to above 100 APSU/ml with minimumof 4 concentrations between 10 and 60 APSU/ml. The viscosity is measuredusing a MIVI 600 from the company Sofraser, 45700 Villemandeur, France.The viscosity is measured as mV after 10 s. For calculation of APSUunits an enzyme standard dilution as described above was used forobtaining a standard curve. The GrafPad Prism program, using a nonlinear fit with a one phase exponential decay with a plateau, was usedfor calculations. The plateau plus span is the mV obtained withoutenzyme. The plateau is the mV of more than 100 APSU and the halfreduction of viscosity in both examples was found to be 12 APSU unitswith a standard error of 1.5 APSU. Enzymes Starch-degrading enzyme:Aquazym 240 L; 240 KNU/g Pectate lyase: Obtained from B. licheniformisas described in U.S. patent 6,124,127; 3000 APSU/g.

[0057] Surfactant

[0058] Rexonic 1218-6 from Huntsman

[0059] Equipment

[0060] Hobart mixer with 4 l vessel and spade mixer.

[0061] Lamort floatation deinking cell, 17 l

[0062] Canadian Standard Freeness Tester.

[0063] TAPPI Handsheet mold.

[0064] TAPPI handsheet press.

[0065] (In both of the above terms, the use of TAPPI is the acceptedabbreviation for the Technical Association of the Pulp and PaperIndustry, Atlanta, Ga. TAPPI maintains a series of standard methods,which are published and entitled “TAPPI Standard Methods”. They areavailable from TAPPI Press, Atlanta, Ga. In the methods below which citea TAPPI Standard Method, reference is automatically made to that methodas published as part of these standard methods.)

[0066] MacBeth Color-Eye 7000 Spectrophotometer.

[0067] Scanner based image analysis system using Optimas software and

[0068] macro developed by Physimetrics, Inc, Roswell, Ga.

[0069] Analysis

[0070] % Brightness was evaluated on the MacBeth Color-Eye 7000Spectrophotometer using TAPPI handsheets made from the pulp in question.In these cases, the wire side of the handsheet was measured while beingbacked by the other handsheets made from the same pulp.

[0071] Residual ink concentration was evaluated with image analysis byscanning the handsheets wet.

EXAMPLE 1

[0072] Enzyme Treatment of Mixed Office Waste

[0073] The waste paper used in process of the invention was mixed officewaste (MOW) collected from recycled office paper bin.

[0074] Repulping

[0075] 140 g of the preprinted, shredded waste paper was added to 700ml, 55θC water in Hobart (water bath at 62.3θC). The paper was agitatedat lowest speed (1) until it was wet. An additional 270 ml of 55θC waterwas added to Hobart. The pulp was mixed well. The temperature and pH wasrecorded. 50 ml of either water or buffer solution containing thedesired amount of enzyme was added to 50 ml of deionised watercontaining 0.05 g surfactant (Rexonic 1218-6, Huntsman) before the wholesolution was added to Hobart. The enzyme solution consisted of a) 0.4kg/ton of air-dry paper starch-degrading enzyme or b) a combination of0.4 kg/ton of air-dry paper starch-degrading enzyme and 0.1 kg/ton ofair-dry paper of pectate lyase. The mixer was run at low speed for 20min. The final temperature and pH was recorded.

[0076] A bucket was filled with 3 l of 55θC water and the pulp was movedfrom Hobart to the bucket. The diluted pulp was stirred in the bucketfor 2 min with an external stirrer.

[0077] Flotation

[0078] 8 l of hot water was added to the deinking cell before the pulpwas added to the cell. More water was added to the cell and the motorwas turned on. The cell was filled to the top until it just began tooverflow. The motor speed was adjusted to 1050-1100 rpm. The flotationprocess was continued for 10 min while skimming foam off top. The pulpwas removed from the cell by draining into a bucket. Rejected ink wasvacuum filtered on a tared filter paper using a Buchner funnel.

[0079] Formation of Handsheets

[0080] After flotation, paper sheets, which weighed between 1.14 g and1.26 g were made from the pulp. The handsheet making procedure generallyfollowed the method spelled out as TAPPI Method T 205 sp-95 (See abovediscussion relating to TAPPI methods). Five mL Lionsurf 66 was added tothe graduated cylinder (25 mg Lionsurf 66/L pulp). The pulp was added tothe Handsheet Mold (HSM) and it was filled with water to the line. Theperforated stirrer was inserted and moved up and down 6 times in about 6ρ 1 s. The stirrer was withdrawn at the top of the 6^(th) stroke. Thedrain was opened after a pause of 5 s. A blotter pad was placed on thehandsheet and covered with couch plate. A couch roll was placed in thecentre of the couch plate and rolled backwards and forwards five timesin 10 ρ 2 s without applying any pressure downwards. The couch roll andplate was removed before the blotter pad was carefully removed carryingthe handsheet along. The blotter pad was placed on a dry blotter on theTAPPI press with the handsheet up. The handsheets were stacked with apolished plate between each. The press was closed and the pressureraised to 50 psig in 30 s and then maintained for another 5 min. Thehandsheets were removed from the press and a dry blotter was placed oneach handsheet. Again the press was closed and a pressure of 50 psig wasmaintained for 2 min. The plates with the handsheets were removed andeach one was placed on a drying ring with the handsheets faced up. Thehandsheets were covered with a piece of filter paper and another ringwas snapped into place. All plates with handsheets were stacked and aweight was placed at the top. The handsheets were left to dry overnight.

[0081] The brightness of the paper sheets was measured in aspectrophotometer and the residual dirt count was determined with imageanalysis by scanning the sheets wet as described above.

[0082] Control sheets were made by the same procedure without addingenzyme. Similarly, sheets were prepared where the enzyme treatment wasreplaced by caustic treatment (0.7% NaOH). Results Residual Ink Averagedirt Brightness concentration size Treatment (%) (ppm) (mm²) None -Control 85.6 8569 0.059 0.7% NaOH 79.5 16789 0.044 a) Starch-degradingenzyme 85.5 9005 0.045 b) Starch-degrading enzyme + 91.4 5514 0.029Pectate lyase

[0083] The present data show that treating with both a starch-degradingenzyme and a pectate lyase during repulping of mixed office waste (MOW)increase brightness, decrease residual ink concentrations and decreasethe average size of dirt particles compared to a treatment withoutenzymes, a conventional treatment (NaOH) or a treatment with only astarch-degrading enzyme.

1. A process for producing a papermaking pulp from starch-containingprinted paper, comprising: a) disintegrating the paper to produce apulp, b) treating with a starch-degrading enzyme and a pectate lyaseduring or after step a), and c) separating ink particles from the pulpafter steps a) and b).
 2. The process according to claim 1 wherein thestarch-degrading enzyme is an alkaline stable enzyme.
 3. The processaccording to claim 1 wherein the starch-degrading enzyme is anΔ-amylase.
 4. The process according to claim 1 wherein thestarch-degrading enzyme is derived from a strain of Bacillus.
 5. Theprocess according to claim 4 wherein the starch-degrading enzyme isderived from B. amyloliquefaciens, B. licheniformis or B.stearothermophilus.
 6. The process according to any of claims 1 to 4wherein the enzymatic treatment is performed with an amount ofstarch-degrading enzyme in the range 0.01-10 KNU/g of dry matter.
 7. Theprocess according to claim 1 wherein the pectate lyase is derived fromor produced by a strain of Bacillus.
 8. The process according to claim 7wherein the pectate lyase is derived from or produced by B.licheniformis.
 9. The process according to any of claims 1, 6 and 7wherein the enzymatic treatment is performed with an amount of pectatelyase in the range 0.01-10 APSU/g of dry matter.
 10. The processaccording to claim 1 wherein the enzymatic treatment is performed at apH in the range 6-10.
 11. The process according to claim 10 wherein theenzymatic treatment is performed at a pH in the range 8-10.
 12. Theprocess according to claim 1 wherein the starch-containing paper ismixed office waste.
 13. The process of claim 1 wherein the enzymetreatment is performed simultaneously with the disintegration.
 14. Theprocess according to claim 13 wherein the enzyme treatment anddisintegration are performed in the presence of a surfactant.
 15. Theprocess according to claim 13-14 wherein the enzyme treatment iscontinued after the disintegration.
 16. The process according to any ofclaims 1 and 13-15 wherein said c) comprises the following sequentialsteps after the disintegration and the enzyme treatment: separation ofink particles, bleaching, and separation of ink particles.
 17. Theprocess according to claim 1 wherein the enzyme treatment is performedafter the disintegration.
 18. The process of any of the preceding claimswherein the enzyme treatment is performed simultaneously with bleaching.19. The process according to claim 18 wherein the enzyme treatment andbleaching are performed in the presence of hydrogen peroxide and asurfactant.
 20. A process for making new paper or tissue fromstarch-containing printed paper, comprising producing papermaking pulpby the process of any preceding claim, and making new paper or tissuefrom the pulp.